Add equal / operator == method

Add thisCap() method to capability servers which returns a capability to itself. Remove CapabilityServerSet's weak pointers since this supersedes them.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=781060

Fix bug in test filters where if you specified only a single test rather than a range, all tests after it in the same file would run.

Fix but where interface server's transitive superclass's methods weren't dispatched correctly -- ouch.

Not everyone has `nproc`. In particular it does not appear to be present on my OSX build. Better to leave a fixed number here. This is just a suggestion anyhow.

This reverts commit 9c18f2ad.

Add asGeneric() methods to generic readers, builders, and interfaces which casts them to the same type but with different generic parameters.

Provide a way to get the ClientHook out of a Capability::Client, needed by third-party RPC/storage/etc systems.

Add CVE numbers to security advisories. Source: http://www.openwall.com/lists/oss-security/2015/03/17/3

Hardcode /bin/cat output option for `capnp compile`.

Implement CapabilityServerSet which provides a way to unwrap loopback capabilities to get the underlying server object, and also implements weak references.

Update comparison blog post to note that proto3 removes unknown field retention, for some ridiculous reason.